Artificial temperature perception neuron based on VO2 volatile memristor

In human sensory system, temperature sensation is also an indispensable sensory ability, besides tactile sensation, which can help the human body respond to the temperature of the outside world so that the central nervous system can initiate a motor response, for example, avoiding injury of the human body. The VO2 device is inherently sensitive to temperature due to its thermally-driven metal-insulator transition,[41, 42] and hence this feature can be exploited to construct an artificial temperature perception neuron, as illustrated in Figure 5a.  Figure 5b firstly shows the I-V characteristics of VO2 volatile memristor at different temperatures ranging from 284 to 306 K, showing apparent impact on the TS characteristics. Only the VO2 device was heated in the probe station during the temperature-elevated test, while the other components were all kept at room temperature. In order to further investigate the impact of temperature on the characteristics of VO2 memristor, critical paramters including Vth and Vhold are extracted. Figure 5c further shows Vth and Vhold values at different temperatures. One can see that both Vth and Vhold decrease as the temperature increases, which agrees with the switching behavior of VO2 observed in the previous study and variation in switching voltages originates from thermal processes induced by Joule heating and its dissipation.[43-46] In order to exclude the possibility of stochastic fluctuations, we have systematically measured the cycle-to-cycle variation of the VO2 memristor under different temperatures (Figure S11). The experimental results in Figure S11 demonstrate that the temperature dependence of the threshold voltages in the VO2 memristor is much more significant than the parameter fluctuations and hence contribute to the temperature sensing capability of the sensory neuron. We have characterized the operation temperature range of our VO2 device. The results demonstrate that the TS characteristics remain stable at least below 0 °C but gradually disappear above 35 °C (Figure S12, Supporting Information), which could be related to the low phase transition temperature of VO2 (~340 K)[47]. This issue can potentially be addressed by using Mott system with higher phase transition temperature, such as NbO2 (~1080 K)[48].
Lee et al.[44] proposed a Joule heating model to  point out that the relationship between Vth, Vhold and temperature (T). In this model, the mott transition occurs when the voltage-induced Joule heating is sufficient to raise the crystal temperature to the mott transition temperature. Assuming the heat obtained in the VO2 crystal is mainly due to the balance between resistive Joule heating and heat loss from the crystal to the environment via heat conduction, this relation can be expressed by the following simple heat equation: